1. Field of the Invention
The present invention relates to a tilt cylinder device for an outboard engine for use on a small boat.
2. Description of the Relevant Art
FIG. 15 of the accompanying drawings shows, in side elevation, an outboard engine for use on a small boat, as disclosed in Japanese Laid-Open Patent Publication No. 60-1097. A pair of laterally spaced stern brackets 502 is fixedly mounted on the stern B of a boat, and a swivel case 504 is supported between the stern brackets 502 by a horizontal pin 503. An outboard engine assembly 501 has an engine body 507 supported by rubber mounts 506a, 506b on a vertical swivel shaft 505 extending through and mounted on the swivel case 504. The swivel case 504 is supported by a tilt cylinder device 510 whose lower end is coupled to the stern brackets 502.
The outboard engine assembly 501 has an engine (not shown) in its upper portion and a propeller 520 on its lower end.
The cylinder device 510 includes a hydraulic cylinder. The engine body 507 is turned upwardly about the pin 503 to the imaginary-line position (FIG. 16) when the boat sails in the shallows or to the solid-line position (FIG. 16) when the boat is grounded or put ashore. The engine body 507 remains held in the elevated position by the tilt cylinder device 510.
The tilt cylinder device 510 is disposed between the stern brackets 502 and the swivel case 504. If the tilt cylinder device 510 is of a large size, then the stern brackets 502 which surround the tilt cylinder device 510 are naturally large in size. It has been desired to reduce the size of the tilt cylinder device and hence the size of the stern brackets.
In the conventional mechanism disclosed in Japanese Laid-Open Patent Publication No. 60-1097, the tilt cylinder device 510 has a cylinder unit and a pressure fluid supply which are juxtaposed within the outer profile of the swivel case, with the longitudinal axis of the cylinder unit being displaced off the longitudinal axis of the swivel case.
Because the cylinder unit and the pressure fluid supply are positioned within the outer profile of the swivel case, any necessary fluid piping may be relatively short. However, the overall configuration of the swivel case is asymmetric since the longitudinal axis of the cylinder unit is positioned out of alignment with the longitudinal axis of the swivel case. As a result, the outboard engine assembly is not well balanced in shape and weight, tending to lower the structural strength of the swivel case. If the mechanical strength of the swivel case is increased, then the weight of the outboard engine assembly is also increased.
The outboard engine assembly that is made of aluminum or aluminum alloy is susceptible to electrolytic corrosion due to continuous contact with seawater. One corrosion-resistant mechanism comprises two anodic metal elements positioned near the propelling screw and at the lower ends of the stern brackets. The anodic metal elements are caused to corrode sooner than the outboard engine body, thereby protecting the outboard engine assembly from corrosion. A relatively large anodic metal element may be attached to the lower ends of the stern brackets.
If a corrosion-resistant mechanism of the above structure were incorporated in the arrangement disclosed in the above publication, then the outboard engine body, the swivel shaft, the swivel case, and the stern brackets would be successively electrically connected by leads. The out-board engine body would be electrically connected to the large-size anodic metal element at the lower ends of the stern brackets by the leads, so that the outboard engine body would be prevented from being corroded over a long period of time.
Since the leads would be interconnected between those members which are relatively movable, they would be exposed and tend to be damaged, making the outboard engine assembly open to attack by corrosion. The exposed leads would easily collect seaweed and dirt, and become unsightly in appearance. In addition, it would be tedious and time-consuming to connect the leads.
Japanese Patent Publication No. 59-5480 shows an outboard engine for small boats. If a lower portion of the disclosed outboard engine hits an underwater obstacle while the boat is sailing, a relief valve in a piston in a tilt cylinder is actuated to move the piston for dampening shocks, so that the outboard engine is prevented from being damaged.
Boats may move forwardly or rearwardly while they are sailing in the shallows. When a boat moves backwards, the lower portion of the outboard engine may be subjected to unexpected forces by an obstacle. The outboard engine disclosed in Japanese Patent Publication No. 59-5480 is, however, not structured for protection against shocks developed by external forces applied when the boat sails backwards.
The present invention has been made in an effort to solve the aforesaid problems and disadvantages of the conventional outboard engines for small boats.